To start succinate dehydrogenase is an enzyme complex which is a catalyst for reactions that occur in the mitochondria. Succinate dehydrogenase (SDH) is also referred to as succinate-coenzyme Q reductase (SQR) or respiratory Complex II but in all cases the term refers to an enzyme complex. Succinate dehydrogenase plays a role in both the Krebs cycle and electron transport where most of the energy is derived from aerobic respiration. Interestingly, if something happens where SDH enzyme malfunctions (a mutation occurs) it sends a signal out of low oxygen. At this point SDH, which plays a role in tumor suppression, ceases to suppress.

The Succinate Dehydrogenase Inhibitor (SDHI) fungicides as a group have been around for a number of years. The first generation types were effective primarily on basidiomycetes like flutolanil (ProStar®) but around 2003 or so the new generation types started to appear on the market which has continued through today. These fungicides are effective on a wide range of turfgrass pathogens.

The SDHI fungicides are absorbed by the plant through the foliage and are systemic in nature (xylem transport primarily). The fungicides are classified as single-site inhibitors. Thus, the potential for pathogen resistance is considered medium to high and the likelihood of cross-resistance among the SDHI fungicides is likely. Although resistance has been reported with pathogens on agricultural production crops, I have at this time found any reports of resistance on turf.

A general use recommendation of these fungicides is to use them judicially and in most cases use them as a preventative or where disease pressure is expected to be moderate. Under more intensive disease pressure, tank mix with an alternative mode of action.

Table 1. SDHI Fungicides Available for Turf (clicking on the Trade Name will link you to the label)